1. Field of the Invention
The present invention relates generally to the field of x-ray imaging machines and systems. More specifically, the present invention pertains to a C-arm x-ray imaging machine incorporating new and improved mechanisms for adjustment and control of the C-arm including a compact yoke for increased overscan.
2. Background of the Invention
It is frequently desired to X-ray a patient from several different positions and is often preferable to do so without the need to reposition the patient. Mobile C-arm x-ray diagnostic equipment, such as that shown in FIG. 1 has been developed to meet these needs and is now well known in the medical and surgical arts. The C-arm x-ray machine is especially useful in that it is small enough and mobile enough to be present in an operating or exam situation without requiring the physician or technician to repeatedly move and without requiring the patient to change positions to obtain a suitable image.
The phrase “C-arm” refers to the movable C-shaped member at one end of the machine. The C-arm contains x-ray source and an image receptor mounted on opposing ends of the C-arm such that x-rays emitted by the source are incident on and detected by the detector. The source and the detector are positioned such that when, for example, a human extremity is interposed between the x-ray source and the image receptor and irradiated with x-rays, the receptor produces data representative of characteristics of the interposed object. The data produced is frequently displayed on a monitor or electronically stored.
The C-arm is normally mounted such that it is permitted two degrees of freedom. First, the C-arm track is slidably mounted to a support member so as to be movable in relation to the support member. This permits the x-ray source and image receptor to be moved rotatably about the arc of curvature of the track in the C-arm. The C-arm support member also permits rotation of the C-arm about its axis. Often the support member is in the general shape of an L and is referred to as the yoke. Mobile C-arms have a third degree of freedom in that they are free to move horizontally along the floor and a fourth in that the C-arm can be raised and lowered.
Obviously, a support structure that permits rotation and movement of such a C-arm must be constructed to withstand large torsional, tensile and compressive stresses. It is also desirable to provide a support that is structure that is heavy enough and that has a center of gravity low enough to avoid tipping when the C-arm and yoke are rotated or raised, which in some cases causes a dramatic shift in the center of mass of the machine.
Additionally, C-arm x-ray equipment must be delicately positioned in order to obtain the image or images desired or required by the physician. Unfortunately, the weight of the support structure makes it difficult to position the C-arm. Therefore, it is desirable to design a source of frictional drag between the C-arm and the support member as well as on the C-arm track.
It is also desirable to balance the C-arm, x-ray source, x-ray detector and yoke so that relatively little physical effort is required to move the C-arm about the orbital rotation axis and the lateral rotation axis. One manner of accomplishing this is to design the C-arm such that its center of mass is as close as possible to the orbital and lateral rotational axes.
Some C-arm designs require a center of mass that is separate from the axis of rotation. In these unbalanced designs, the user must exert significant force to rotate the apparatus. This physical exertion generally detracts from other, more significant tasks that a health care provider may be undertaking. Also, unbalanced designs can be dangerous to both the operator and the patient. For example, unbalanced C-arms require much more powerful braking systems. Without an adequate braking system, the C-arm could unexpectedly rotate downwardly and strike an individual. Accordingly, a completely balanced C-arm x-ray imaging system is difficult to design at best.
Previous C-arm x-ray machines required the removal of the C-arm in order to service or replace the brake means. Other C-arms require the user to remove the back of the yoke to repair or replace the brake. Both processes are cumbersome and time consuming. Additionally, prior devices were difficult to maintain sterile environment.
The term “overscan” is the extent to which a C-arm is permitted to rotate beyond the vertical beam configuration. Overscan is limited in machines that are configured with conventional yokes. Customers generally prefer increased overscan because they can image the patient more easily with fewer positional adjustments to the machine. The degree of overscan is generally limited by either the x-ray source or the x-ray detector colliding with the yoke. Design guidelines also require additional clearance on each side of the yoke to avoid the danger of pinch points. In the preferred embodiment, each extra inch of clearance translates to an almost 3 degree difference in overscan.